University of Kentucky UKnowledge Physiology Faculty Publications Physiology 12-2017 Sustained Sensitizing Effects of Tumor Necrosis Factor Alpha on Sensory Nerves in Lung and Airways Ruei-Lung Lin University of Kentucky, [email protected] Qihai Gu Mercer University Mehdi Khosravi University of Kentucky, [email protected] Lu-Yuan Lee University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits oy u. Follow this and additional works at: https://uknowledge.uky.edu/physiology_facpub Part of the Pharmacology Commons, Physiology Commons, Pulmonology Commons, and the Therapeutics Commons Repository Citation Lin, Ruei-Lung; Gu, Qihai; Khosravi, Mehdi; and Lee, Lu-Yuan, "Sustained Sensitizing Effects of Tumor Necrosis Factor Alpha on Sensory Nerves in Lung and Airways" (2017). Physiology Faculty Publications. 139. https://uknowledge.uky.edu/physiology_facpub/139 This Article is brought to you for free and open access by the Physiology at UKnowledge. It has been accepted for inclusion in Physiology Faculty Publications by an authorized administrator of UKnowledge. For more information, please contact [email protected]. Sustained Sensitizing Effects of Tumor Necrosis Factor Alpha on Sensory Nerves in Lung and Airways Notes/Citation Information Published in Pulmonary Pharmacology & Therapeutics, v. 47, p. 29-37. © 2017 Elsevier Ltd. All rights reserved. This manuscript version is made available under the CC‐BY‐NC‐ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/. The document available for download is the author's post-peer-review final draft of the ra ticle. Digital Object Identifier (DOI) https://doi.org/10.1016/j.pupt.2017.06.001 This article is available at UKnowledge: https://uknowledge.uky.edu/physiology_facpub/139 HHS Public Access Author manuscript Author ManuscriptAuthor Manuscript Author Pulm Pharmacol Manuscript Author Ther. Author Manuscript Author manuscript; available in PMC 2018 December 01. Published in final edited form as: Pulm Pharmacol Ther. 2017 December ; 47: 29–37. doi:10.1016/j.pupt.2017.06.001. Sustained sensitizing effects of tumor necrosis factor alpha on sensory nerves in lung and airways Ruei-Lung Lin1, Qihai Gu2, Mehdi Khosravi3, and Lu-Yuan Lee1 1Department of Physiology, University of Kentucky, Lexington, Kentucky, USA 2Department of Biomedical Sciences, Mercer University, Macon, Georgia, USA 3Department of Medicine, University of Kentucky, Lexington, Kentucky, USA Abstract Tumor necrosis factor alpha (TNFα) plays a significant role in the pathogenesis of airway inflammatory diseases. Inhalation of aerosolized TNFα induced airway hyperresponsiveness accompanied by airway inflammation in healthy human subjects, but the underlying mechanism is not fully understood. We recently reported a series of studies aimed to investigate if TNFα elevates the sensitivity of vagal bronchopulmonary sensory nerves in a mouse model; these studies are summarized in this mini-review. Our results showed that intratracheal instillation of TNFα induced pronounced airway inflammation 24 hours later, as illustrated by infiltration of eosinophils and neutrophils and the release of inflammatory mediators and cytokines in the lung and airways. Accompanying these inflammatory reactions, the sensitivity of vagal pulmonary C- fibers and silent rapidly adapting receptors to capsaicin, a selective agonist of transient receptor potential vanilloid type 1 receptor, was markedly elevated after the TNFα treatment. A distinct increase in the sensitivity to capsaicin induced by TNFα was also observed in isolated pulmonary sensory neurons, suggesting that the sensitizing effect is mediated primarily through a direct action of TNFα on these neurons. Furthermore, the same TNFα treatment also induced a lingering (> 7days) cough hyperresponsiveness to inhalation challenge of NH3 in awake mice. Both the airway inflammation and the sensitizing effect on pulmonary sensory neurons caused by the TNFα treatment were abolished in the TNF-receptor double homozygous mutant mice, indicating the involvement of TNF-receptor activation. These findings suggest that the TNFα-induced hypersensitivity of vagal bronchopulmonary afferents may be responsible for, at least in part, the airway hyperresponsiveness caused by inhaled TNFα in healthy individuals. Keywords asthma; airway inflammation; TRPV1; cough; mouse Corresponding author: Lu-Yuan Lee, Ph.D., Department of Physiology, University of Kentucky Medical Center, Lexington, Kentucky 40536-0298, USA, Telephone: 859-323-6339, [email protected]. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Lin et al. Page 2 Author ManuscriptAuthor Introduction Manuscript Author Manuscript Author Manuscript Author An important role of tumor necrosis factor alpha (TNFα), a pro-inflammatory cytokine, in the pathogenesis of airway inflammatory diseases such as allergic asthma has been extensively documented [1–5]. TNFα was detected in bronchoalveolar lavage fluid, exhaled breath condensate and sputum of asthmatic patients during acute exacerbation or after antigen inhalation challenge in these patients [6,7]. TNFα is released from a variety of cell types in the airways, such as mast cells and macrophages, via the immunoglobulin E- dependent mechanism [2,5,8,9]. Once released, TNFα can exert multiple effects on a number of effector cells and induce the inflammatory reaction in the airways. Inhalation of aerosolized TNFα induced bronchial hyperresponsiveness accompanied by airway inflammation in healthy human subjects [10], but the underlying mechanism was not fully understood. One of the prominent pathophysiological features of inflammation-induced bronchial hyperresponsiveness is a heightened sensitivity of airway sensory nerves [11,12]. Previous investigators have repeatedly reported that TNFα induced a potent sensitizing effect on dorsal root ganglion (DRG) and trigeminal ganglion nociceptive neurons, leading to the development of lingering inflammatory pain in various somatic tissues [13–16]. This hyperalgesic effect was mediated through an action on the TNF receptors, TNFR1 and TNFR2, located on the cell surface, which resulted in an increase in the sensitivity and/or expression of transient receptor potential vanilloid type 1 (TRPV1) receptors expressed in these nociceptive neurons [3]. For example, in isolated DRG neurons, pretreatment with TNFα for a short-duration (60 s) immediately and reversibly increased the current amplitude evoked by activation of TRPV1 receptors, and this rapid and transient sensitizing effect of TNFα was attenuated by deletion of the TNFR2 gene [17]. On the other hand, exposure of DRG neurons to TNFα for a longer duration (48 hours) induced a pronounced increase in the proportion of DRG neurones expressing TRPV1 receptor-like immunoreactivity [18]. Interestingly, the TNFα-induced TRPV1 expression was clearly increased in the medium- and large-size neurons that normally do not exhibit TRPV1 sensitivity; and this effect of TNFα was absent in the DRG neurons isolated from mice lacking TNFR1 [18]. The C-fiber sensory nerves are the dominant subtype of vagal afferents innervating the entire respiratory tract in various mammalian species including mice [19–21]. Increasing evidence suggests that activation of these bronchopulmonary C-fiber afferents is responsible for the manifestation of various symptoms in the airway inflammatory diseases [11,12]. An abundant expression of TRPV1 in the neuronal soma and sensory terminals is a reliable and prominent biomarker of these C-fiber afferents [22,23]. More importantly, recent studies have shown that chronic airway inflammation upregulated the sensitivity and expression of TRPV1 in these sensory nerves innervating the airways and lungs [24,25]. In the light of these previous findings, we recently carried out a series of studies aimed to investigate if airway delivery of TNFα induced airway inflammation and elevated the TRPV1 sensitivity of bronchopulmonary sensory nerves; and if so, whether the sensitizing effect of TNFα was mediated through its action on TNFRs. Mouse was chosen as the animal species for these studies so that the involvement of TNFRs could be evaluated in TNF- receptor double homozygous mutant mice (TNF−/−). Experimental methods, protocols and Pulm Pharmacol Ther. Author manuscript; available in PMC 2018 December 01. Lin et al. Page 3 results of these studies have been reported in details in our recent publications [26–28], and Author ManuscriptAuthor Manuscript Author Manuscript Author Manuscript Author a collected summary of this series of studies is presented in this mini-review. Airway inflammation induced by TNFα TNFα released from mast cells, macrophages and other inflammatory cells can trigger diverse and potent inflammatory responses in the airways. Activation of TNFRs by TNFα can cause a chemotactic action, upregulate the leukocyte-endothelial cell adhesive molecules E-selectin and vascular cell adhesion molecule-1, which in turn can enhance the production of Th2 cytokines and cause infiltration and